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Car Forum / Volvo Cars / January 2006recommended rpm
Can one do damage driving at low rpm's? My wife likes to drive our 86 740 turbo at sub 2000 rpm in OD, I suspect using the turbo to compensate. It bugs me, but can it really do harm? It's a second hand car, so I don't have a manual. > Can one do damage driving at low rpm's? My wife likes to drive our 86 > 740 turbo at sub 2000 rpm in OD, I suspect using the turbo to > compensate. It bugs me, but can it really do harm? > > It's a second hand car, so I don't have a manual. It should carbon up, use more fuel and possibly overheat. Oil won't pump with enough pressure for the work being asked of the motor, so it won't last as long. But it's hard to prove all that to someone who doesn't understand and God protects fools, women and drunks. > Can one do damage driving at low rpm's? My wife likes to drive our 86 > 740 turbo at sub 2000 rpm in OD, I suspect using the turbo to > compensate. It bugs me, but can it really do harm? > > It's a second hand car, so I don't have a manual. I usually try to keep it under 2000 RPM cruising, though that's not always possible. It's best to just drive it by feel, if it's lugging or vibrating excessively then downshift to raise the RPM. So long as your engine isn't pinging or rattling. If so you should be using a better grade of gas. Cars with an ecm should make the fuel richer to prevent detonation. What does it hurt? > Can one do damage driving at low rpm's? My wife likes to drive our 86 > 740 turbo at sub 2000 rpm in OD, I suspect using the turbo to > compensate. It bugs me, but can it really do harm? > > It's a second hand car, so I don't have a manual. It does go into the yellow zone on the turbo dial, which worries me because I've heard overuse of the turbo can wreck the engine. The previous owner says his teenage kids blew two motors! But what's the difference between a teenaged boy driving it hard, and my wife low-rpming it up the hills with the turbo in yellow? > It does go into the yellow zone on the turbo dial, which worries me > because I've heard overuse of the turbo can wreck the engine. The > previous owner says his teenage kids blew two motors! But what's the > difference between a teenaged boy driving it hard, and my wife > low-rpming it up the hills with the turbo in yellow? Boy Racers (of whatever age) tend to rev the engine high and long, and this is harder on turbos than having to operate at low speeds and higher pressures. Do these engines even increase the turbo pressure that much under low-speed load...?  Signaturehttp://freevision.org/michael/index.html How could reving high be hard on the turbo if the turbo dial is showing a lower reading for the same speed? I assume the turbo dial is pressure, but I don't know. The particular circumstance is driving on the highway around 90km per hour, in OD, around 1800 rpm, then not gearing down for hills, and the turbo going way into the yellow until back on the flat. When I drive, I gear down for hills, the engine revs are higher (2500ish) but the turbo reading is much lower, well below the yellow. > How could reving high be hard on the turbo if the turbo dial is showing > a lower reading for the same speed? I assume the turbo dial is > pressure, but I don't know. For a given pressure, higher revs result in more heat and more wear on the turbo. I doubt it glows dull red when run under load at low speeds like it can at high speeds. > The particular circumstance is driving on the highway around 90km per > hour, in OD, around 1800 rpm, then not gearing down for hills, and the > turbo going way into the yellow until back on the flat. > > When I drive, I gear down for hills, the engine revs are higher > (2500ish) but the turbo reading is much lower, well below the yellow. As noted elsewhere, if it isn't pinging, she probably isn't damaging it. You may want to see if you can adjust the wastegate to limit the boost. Signaturehttp://freevision.org/michael/index.html > How could reving high be hard on the turbo if the turbo dial is showing > a lower reading for the same speed? I assume the turbo dial is > pressure, but I don't know. Because the boost guage is showing just that, pressure. If the engine is revving higher the turbo has to spin faster to maintain the same boost. Really though either scenario will not hurt the turbo, it should last a long time regardless of how it's driven as long as it's well maintained and doesn't get extreme abuse. Ultimately, turbo or not, anytime you pull to much hp at too low of an rpm, out of an engine, the likelyhood of detonation increases. (Also the temperature rise of the intake air aggrevates this situation.) That will damage an engine. Modern cars enrichen the mixture to decrease this from happening. I don't know what sort of hills your driving on. If you hear pinging or a rattling sound during this event you are damaging the engine. The exhaust gas temperature also goes way up and can cook older turbochargers. I don't know what is in your car. I do suspect though, she is asking a bit too much to be in overdrive going uphill. Especially some hills I have in mind. > How could reving high be hard on the turbo if the turbo dial is showing > a lower reading for the same speed? I assume the turbo dial is [quoted text clipped - 6 lines] > When I drive, I gear down for hills, the engine revs are higher > (2500ish) but the turbo reading is much lower, well below the yellow. >Ultimately, turbo or not, anytime you pull to much hp at too low of an >rpm, out of an engine, the likelyhood of detonation increases. (Also the [quoted text clipped - 6 lines] >she is asking a bit too much to be in overdrive going uphill. Especially >some hills I have in mind. Maybe she needs this: http://www.viatrack.ca/ Regards, Boris Mohar Got Knock? - see: Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca void _-void-_ in the obvious place >> How could reving high be hard on the turbo if the turbo dial is showing >> a lower reading for the same speed? I assume the turbo dial is [quoted text clipped - 6 lines] >> When I drive, I gear down for hills, the engine revs are higher >> (2500ish) but the turbo reading is much lower, well below the yellow. > Boy Racers (of whatever age) tend to rev the engine high and > long, and this is harder on turbos than having to operate at low > speeds and higher pressures. Do these engines even increase the > turbo pressure that much under low-speed load...? The turbo pressure will increase to the full 8.5 PSI at any speed if you give it enough gas. The pressure is always whatever the guage shows regardless of RPM, though the guage is not calibrated. The difference is that the turbo will be spinning faster to maintain any given pressure at a higher RPM as more air will be flowing through the motor. > It does go into the yellow zone on the turbo dial, which worries me > because I've heard overuse of the turbo can wreck the engine. The > previous owner says his teenage kids blew two motors! But what's the > difference between a teenaged boy driving it hard, and my wife > low-rpming it up the hills with the turbo in yellow? Using the turbo a lot will consume more fuel and cause more wear on the turbo, but you really have to try in order to blow a Volvo motor. I don't know what the teenagers could have been doing other than possibly constant redlining the RPM or messing with the boost. I drive mine fairly hard and have yet to damage even a high mileage motor. Generally you want to keep the needle in the black unless you need the power, boost won't hurt it but it won't help the economy any since the ECU richens the mixture under boost. Yes if it is going that high I imagine it could hurt the engine. Especially on that year I am not sure there is anything to enrichen the mixture to protect the engine. I don't know. Using premium gas will help to protect the motor. If she scraps the motor, you will really have something on her for a long time! > It does go into the yellow zone on the turbo dial, which worries me > because I've heard overuse of the turbo can wreck the engine. The > previous owner says his teenage kids blew two motors! But what's the > difference between a teenaged boy driving it hard, and my wife > low-rpming it up the hills with the turbo in yellow? > Can one do damage driving at low rpm's? My wife likes to drive our 86 > 740 turbo at sub 2000 rpm in OD, I suspect using the turbo to > compensate. It bugs me, but can it really do harm? > > It's a second hand car, so I don't have a manual. FWIW, the 740 series water cooled turbos are remarkably robust. I couldn't convince my wife (who was the primary driver of our '85 765T for more than a decade) not to rev the engine when she started it or to let the turbo cool down when pulling off the freeway into a gas station. I could hear the turbo spinning down as she got out of the car. At nearly 240K miles it is still going, and the engine has never been apart beyond timing belt replacements. Your wife is more valuable than the car, so relax and enjoy the ride. Mike In general high revs wear the top end of the engine (rings, cams and valves) whereas low revs wear the bottom end of the engine (bearings). As long as the engine isn't lugging it should be ok although personally I tend to keep the revs between 2000-3000 for general driving (S70 T5). > Can one do damage driving at low rpm's? My wife likes to drive our 86 > 740 turbo at sub 2000 rpm in OD, I suspect using the turbo to > compensate. It bugs me, but can it really do harm? > > It's a second hand car, so I don't have a manual. |
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